"My plans include an underground electric fence, with helicopter stations to respond quickly to breaches of the border."

However, Paul won't comment on what exactly that means. Since it would be unfair not to speculate, that's what Stein does: making a series of assumptions about what it would consist of in order to try to portray Paul as a border extremist. He doesn't reveal that at least two of his sources aren't exactly strong opponents of illegal immigration:

when approached in the halls of Senate several weeks ago and asked about the idea (though not told who proposed it), National Republican Senate Committee Chair John Cornyn (R-Tex.) assumed it was a joke... "I have not heard that," the Texas Republican said. "Underground? What would happen? How would that work?"

See his name's link and do a search here for more on him. However, not revealing how the other quote source's opinions contrast with those of Paul is much more questionable on Stein's part:

Some elaboration on the concept is needed because even respected immigration experts -- including those from libertarian backgrounds (as is Paul) -- say they're in the dark... "Kind of an interesting idea," Daniel Griswold of the CATO Institute said sarcastically. "I haven't heard of it... ..."They are going across very sensitive land along the Rio Grande River," said CATO's Griswold. "They are going across land for ranchers -- it is running roughshod over private property rights which kind of shocks me that Rand Paul would embrace this concept with the eminent domain issues it entails." ...But mainly, Griswold notes, it's incredibly expensive. Rep. King said that his proposal would have cost $1.3 million per mile and up to $680 million total. That was the congressman's own, rosy estimate. And that was for a fence built over ground. Paul's underground fest would, in all likelihood, range well over $1 billion.

What Stein doesn't reveal is that Dan Griswold is an open or very loose borders extremist. He's naturally going to be opposed to any form of fencing since he sees no reason why we shouldn't have open or very loose borders.